To test the hypothesis that episodic hypoglycemia increases the frequency of subsequent iatrogenic hypoglycemia in the clinical setting in patients with IDDM, the frequency of asymptomatic (biochemical) symptomatic and severe iatro-genic hypoglycemia is determined in patients with IDDM during a 4 week period of clamped hypoglycemia (approx. 2.8 mmol/L x 2h twice weekly) and during a 4 week period of otherwise identical clamped hypoglycemia (approx. 8.3 mmol/L x 2h twice weekly.)